Single-Slope Steel Buildings: Design and Uses

A single-slope steel building has a roof that falls in one direction, from a high sidewall to a low sidewall. The frames may be clear span or multi-span, and all rainwater drains to one side, which suits sites with a single drainage route, retail frontages and buildings placed against boundaries.

Key facts

One high sidewall and one low sidewall, with no ridge.
All roof water drains to the low side.
Frames can be clear span or multi-span.
The tall wall is often used for signage or a modern facade.
Roof run to the gutter is the full width, which affects gutter size.

How is a single-slope building framed?

The rafter runs from the low eave to the high eave in one plane. Columns at each sidewall have different heights, and the frame is designed with moment connections to resist both gravity and lateral loads.

For wider buildings, interior columns can support the rafter to reduce its span, in the same way as a multi-span gable frame. The frame geometry is asymmetric, so the base reactions differ at each side.

When is a single slope the best choice?

A single slope is useful when drainage can only go to one side, when the building stands next to a boundary or another structure, or when a tall front elevation is wanted for retail or showroom use.

It is also used for small buildings such as service stations, sheds, and building additions, and for roofs designed to carry solar panels facing one direction.

Drainage and roof slope

Because all water flows to one gutter, the gutter and downspouts must be sized for the full roof area. The long roof run also increases the volume of water at the low edge during heavy rain.

The slope chosen balances drainage, wall height and cost. Low slopes reduce the height of the high wall but need careful attention to panel laps and end laps, so the roof panel type should suit the slope.

Design points to watch

Wind and snow loads on single-slope roofs differ from gable roofs, and snow can drift against higher adjacent structures. These effects are taken from the governing load code by the project engineer.

The high sidewall has larger wall area and taller columns, which affects girt and bracing design. Openings in the tall wall should be fixed early so framing and bracing are arranged around them.

Points to confirm with your engineer

Which sidewall is high and which is low, and why.
Clear height required at the low sidewall.
Rainfall intensity and the downspout discharge points.
Snow drift against adjacent higher structures.
Roof panel type suitable for the chosen slope.
Signage, solar or parapet loads on the high wall or roof.

Frequently Asked Questions

Is a single-slope building cheaper than a gable building?

Not always. For narrow buildings it can be economical, but the taller high wall and the larger gutter can offset savings. Compare both options for your width and loads.

Which side should be the high side?

It depends on drainage routes, site boundaries, the main facade and solar orientation. Choose it during concept design with the architect and engineer.

Can a single-slope building be multi-span?

Yes. Interior columns can support the rafter so wider single-slope buildings remain economical.

Engineering content is general guidance. Every World Steel building is designed by qualified engineers to the code and loads of the project.